In steer-by-wire steering systems, the position of the steered wheels is not directly coupled to the steering wheel. There is a connection between the steering wheel and the steered wheels by means of electrical signals. Instead of the mechanical coupling, a wheel angle adjuster is used for positioning the wheels and a manual force actuator is used for simulating the restoring forces on the steering wheel.
To increase the driving safety of a motor vehicle in road traffic, modern motor vehicles comprise an increasing number of driver assistance systems that are arranged to increase active safety. Besides speed regulations and separation regulations that are partly combined therewith, lane holding systems are also known.
For said systems, steering wheel monitoring is important that determines whether there is driver activity on the steering wheel or not.
In this case, a situation in which the driver has gripped the steering wheel is referred to below as a hands-on situation, and a situation in which the driver has not gripped the steering wheel is thus referred to as no-hands driving, as a hands-off situation, which corresponds to the terms used in this technical area.
From DE 10 2009 028 647 B3, hands-on/off detection of an electrically assisted steering system is known. The detection of the driver activity on the steering wheel is carried out by means of a test signal. In this case a monitor generates a model from the test signal and the torque of the steering wheel.
DE 10 2010 019 236 B3 also discloses a method for measuring a hand touching a helicopter control. In this case, a frequency spectrum is determined from movement signals of the control, whereby it can be detected whether the driver is in contact with the control. In addition, vibrations in the surroundings of the control are detected. The frequency spectrum with the control not being touched differs from the frequency spectrum when a control is being touched. However, said methods have the disadvantage that they do not always have the desired accuracy.
Thus a need exists for a steer-by-wire steering system for motor vehicles with more accurate, sufficiently faster and always reliably working steering wheel monitoring.